Improve test framework: tfw_cat --hexdump, TFWSTDOUT

Add -h|--hexdump option to tfw_cat() and fix faulty logic in tfw_cat()
-v option wof files not ending in \n (newline)

Add TFWSTDOUT and TFWSTDERR env vars set by execute() with absolute
path names of files containing stdout and stderr respectively (as an
alternative to using replayStdout() and replayStderr()).
Improve Rhizome testdefs: add rhizome_list_unpack()

Makes all the output of a "rhizome list" command available in shell
variables